It has been believed that the injection molding of thinwalling articles by numerous different olefinic polymers and/or blends required the use of polymers having both (1) a very high melt index (I.sub.2) (e.g., I.sub.2 of greater than about 30 grams/10 minutes, usually about 100 grams/10 minutes) in order to fill a multiple cavity mold and thus reduce the cycle time, as in contrast to the use of very low I.sub.2 (less than about 2 grams/10 minutes) resins, and (2) a narrow molecular weight distribution (indicated by a low value of weight average molecular weight divided by number average molecular weight (M.sub.w /M.sub.n), as opposed to broad molecular weight distribution, in order to obtain the best molded article.
For example, Modern Plastics International, p. 81 (August, 1983) discloses that the "super high flow" polyethylene resins having a melt index (I.sub.2) of 100 grams/10 minutes and higher can reduce the cycle time for thinwalling injection molding applications.
Modern Plastics, pp. 46-49 (June 1990), discloses that both The Dow Chemical Company and Occidental Chemical Co. are capable of making "asymmetrical shaped" high density polyethylene (HDPE) resins. Dow's asymmetrical shaped resins are said to process like a resin having I.sub.2 of 100 grams/10 minutes, yet retain physical properties like a resin having I.sub.2 of 40 grams/10 minutes.
U.S. Pat. Nos. 4,192,935 and 4,294,794, incorporated herein by reference, each disclose an olefinic copolymer having a density of 0.940-0.960 grams/cubic centimeter, a melt index in the range of 100-200 grams/10 minutes, and a M.sub.w /M.sub.n ratio of less than 5 for use in injection molding of thinwalling articles.
U.S. Pat. No. 5,015,511 (Treybig et al), incorporated herein by reference, discloses olefinic polymers having a melt index in the range of 80-200 grams/10 minutes, melt flow ratio (I.sub.10 /I.sub.2) in the range of 7.2 to 14, a M.sub.w /M.sub.n ratio in the range of 6.7-14.6 and a density in the range of 0.925 to 0.940 grams/cubic centimeter which are used for injection molding of thin walled containers with a thickness in the range of 0.15 mm to 1.5 mm.
It has now been discovered that certain types of articles can be successfully prepared by injection molding of olefinic polymers and virgin polymers/recycled polymer blends having: (1) a melt index (I.sub.2) from about 0.1 to about 2 grams/10 minutes and, (2) extremely broad molecular weight distributions (high M.sub.w /M.sub.n ratios and high I.sub.10 /I.sub.2 ratios) with very strong mechanical properties.